Inexpensive casters capable of carrying substantial loads and yet allowing free swiveling movement are purposely designed with a great deal of play in their swivel mechanism to cut down on manufacturing costs and to prevent binding of the swivel mechanism. Consequently, these casters have an inherent tendency to flutter when the castered device is pushed in a straight line under light-load or no-load conditions -- a noisy and highly undesirable phenomenon.
Fluttering can be avoided, of course, by using precision bearings built to close tolerances, but this is an expensive alternative which is economically unacceptable in most instances. Reduction of the play in the swivel mechanism has been attempted in the prior art by simply loading the bearings at the cone (e.g. by springs or other resilient means), but this did not fully solve the problem because systems of this type tended to allow the fork to tilt so much under load that the bearing balls could roll out of their races.
In those applications where fluttering presents significant noise, maintenance, or safety problems, and where steering control is necessary, solutions such as that of U.S. Pat. No. 3,924,292 have been proposed in special situations. For wide usage of any flutter-eliminating scheme where no steering control is needed, however, a simpler, more universally applicable approach was still needed.